It won't influence buying decisions you are right. But, it might affect the number of people who find you. A high PR should in theory mean more exposure from Google and hence in theory should get you more visitors. As long as you are doing what needs to be done to convert visitors to customers, then PR will help indirectly.

Yes, somehow I think PR does matters when you want to sale your site. Also, some CPC, CPM ads companies determines your site through PR.

i see site withlower page ranks constitly rank higher on very competitive keywords

Rank is still rank, the most important is the site can bring out wha you want to tell.

page rank is not important as it ca be bosted artificaly